Read from text file between header and footer
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Is there an easy way to read numerical data from a text file below a 3 line header and above a footer starting with a sequence of asterisks. The data is in 3 complete columns of unknown length. Delimiter and asterisks can be modified if necessary.
Tried readtable but footer is causing problems as there doesn't appear to be an option from detectImportOptions.
see attached for example data file
ld dim real
ratio ht speed
[] [s] [m/s]
5.0000000e-01 3.4497665e+02 2.1712214e+03
1.0000000e+00 3.8184070e+02 2.3923590e+03
1.5000000e+00 3.9916530e+02 2.4919967e+03
2.0000000e+00 4.0763144e+02 2.5342191e+03
2.5000000e+00 4.1118036e+02 2.5473084e+03
...
**********************************************
2.8682373e+00 4.1181815e+02
2.6080322e+00 2.5476604e+03
Accepted Answer
Star Strider
on 16 Oct 2023
Edited: Star Strider
on 16 Oct 2023
type('data.txt')
fidi = fopen('data.txt','rt')
C = textscan(fidi, '%f%f%f', 'HeaderLines',3, 'CollectOutput',1)
fclose(fidi);
A = cell2mat(C)
figure
plot(A(:,1), A(:,[2 3]))
grid
It will stop automatically at the line of asterisks, however if you want to re-start it to read the last two lines, that is an option.
.
4 Comments
Brantosaurus
on 16 Oct 2023
My pleasure!
That becomes slightly more involved for this specific file —
fidi = fopen('data.txt','rt');
k1 = 1;
while ~feof(fidi)
if k1 == 1
C = textscan(fidi, '%f%f%f', 'HeaderLines',3, 'CollectOutput',true, 'Delimiter','\t');
else
C = textscan(fidi, '%f%f%f', 'HeaderLines',1, 'CollectOutput',true, 'Delimiter','\t');
end
A = cell2mat(C);
if isempty(A) %find( Empty Matrix Indicates End-Of-File
break
end
D{k1,:} = A;
fseek(fidi, 0, 0);
k1 = k1 + 1;
end
fclose(fidi);
Out = cell2mat(D);
D{1}
D{2}
figure
hold on
for k = 1:numel(D)
plot(D{k}(:,1), D{k}(:,[2 3]), 'DisplayName',"Section "+k)
end
hold off
grid
legend('Location','best')
The only problem is in the second part, where it does not fill the missing value with NaN in the second line. There apparently is no provision in textscan to fill the empty positions, so it just concatenates them into a (2x2) matrix rather than a (2x3) with the missing values as NaN.
opts = fixedWidthImportOptions('NumVariables',3, 'VariableWidths',[15 16 16], 'DataLines',[4 25; 27 28]);
T1 = readtable('data.txt', opts)
T1(end-1:end,:)
missing = varfun(@ismissing, T1);
missing(end-1:end,:)
T2 = varfun(@(x)fillmissing(x,'constant',{'NaN'}), T1)
T2(end-1:end,:)
format long
A = str2double(table2array(T2))
A(end-1:end,:)
... and we have liftoff!
(It took a few minutes for me to surf the fixedWidthImportOptions documentation because I don’t use it very often, then experiment until I got the result I wanted.)
.
Brantosaurus
on 16 Oct 2023
Thank you.
The fseek call moves to the next position in the file, beyond the non-numeric text tthat stopped textscan.
If you have more of these files, use readtable with fixedWidthImportOptions, as I did here, in the last part of my previous Comment. That includes inserting the NaN value in the blanks.
Reprising that section here —
opts = fixedWidthImportOptions('NumVariables',3, 'VariableWidths',[15 16 16], 'DataLines',[4 25; 27 28]);
T1 = readtable('data.txt', opts)
T1(end-1:end,:)
% missing = varfun(@ismissing, T1);
% missing(end-1:end,:)
T2 = varfun(@(x)fillmissing(x,'constant',{'NaN'}), T1)
T2(end-1:end,:)
format longG
A = str2double(table2array(T2))
A(end-1:end,:)
You would need to manually keep track of the number of lines after the asterisks line (here the last two), and make approipriate changes to the 'NumVariables', 'VariableWidths', and 'DataLines' name-value pairs in the fixedWidthImportOptions call, however that should be straightforward.
I no longer have access to R2017a, and while there used to be online documentation for a few previous releases, that appears to no long be an option. Everything I have listed here should be available in — and compatible with — R2017a, however I cannot check to be certain.
.
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